The aerial advertising firm AirSign confirmed to NBC News that the pilot escaped from one of its blimps and that no other person was on board. The blimp, which was advertising a local credit union, wasn't affiliated with the United States Golf Association (USGA).

Airsign's president, Patrick Walsh, told NBC affiliate WTMJ of Milwaukee that the crash likely occurred because of a catastrophic failure of its skin, an "envelope" that is inflated by using air heated by propane burners.

The USGA said the blimp caught on fire and went down in a field about a half-mile from the Erin Hills golf course at 11:15 a.m. CT (12:15 p.m. ET).

First responders already at the tournament arrived at the crash site quickly to treat the pilot, the USGA said. No one on the ground was hurt.

The pilot, Trevor Thompson. sustained serious injuries and burns and was airlifted to a hospital, the Washington County Sheriff's Office said. Described as an experienced and careful pilot by Walsh, Thompson sustained burns on 40 percent of his body because of the crash, WTMJ reported.

"He wore a fireproof flight suit, and that probably protected him quite a bit as well,” Walsh told WTMJ.

The Froedtert & the Medical College of Wisconsin Hospital said in a statement that Thompson remains in serious condition at their hospital in Wauwatosa.

The blimp had been airborne for "several hours" when it crashed and was lawfully operating at the proper altitude, authorities said.

The Federal Aviation Administration and the National Transportation Safety Board were assisting in the investigation.